Quoting bass pumped <[EMAIL PROTECTED]>:
> > > > I built a DATCOM model for the A380, and passed it to Jon
> > > Berndt. He
> > > > is probably off-line for a day to two. I'm sure he will
> > > respond when
> > > > he gets a chance, updating us on the status of the A380 model.
> > >
> > > You should send in your FDM so that it can be included in the CVS.
> > >
> > > Ampere
> >
> > Let me check with the Chief to see what happened with that little project.
> > Jon, you out there?
>
> Sorry, complete out of topic, but how do you build a DATCOM model for
> an aircraft?
DATCOM is a computer program for generating aerodynamic coefficients and
stability derivatives based on the aircraft geometry properties. Much of the
information can be obtained from a book like Jane's All The World's Aircraft,
but there is also a lot of guessing involved too. Having a good (accurate)
three-view drawing, you end up measuring a lot of stuff. For example, you would
need to know, be able to measure, or guess at:
o wing span, area, and sweep
o airfoils for wing, vertical, and horizontal tail
o center of gravity in three axes
o geometric distances like cg to root of vertical tail, horizontal
tail, etc.
o control surface areas, locations, and deflections (elevator, aileron,
not rudder, flaps, slats, etc.)
o fuselage cross-sectional characteristics at various stations
For the A380, I had no idea what the airfoil sections were, and DATCOM allows
only a root and tip airfoil anyway. I guessed at something. Will the results
show the 0.5% fuel efficiency that Airbus engineers worked so hard to obtain?
Nope. Will it give something that isn't too bad? Yep.
The work that I've done with DATCOM has yielded some pretty amazing results, at
least I was amazed. I would say that it is possible to obtain results withing 2-
5% of actual flight test results, although I haven't done any specific
evaluation to decided just how close it really is. With flight test data, one
would go in and tweak coefficient tables to get closer results.
If there isn't a flight package available from the manufacturer (like for an
old aircraft), or the price is prohibitive (think in the hundreds of thousands
of dollars or more) for your intended use (a free simulator like FlightGear
can't afford a flight package), this is a good way to get started.
I have flight test data from a couple of aircraft. One was the Cessna Citation.
I checked a couple tests, and the results were impressive. I want to run all of
the tests one of these days and compare the results to the flight test data. I
also want to do a B737 model one of these days. All I need to do is quit my day
job, throw the girlfriend out, and win the lottery ;-} (Wait, I'll keep the
girlfriend, she just needs to get another job.)
[Shameless promotion incoming] If you are interested in exploring the wonderful
of DATCOM, you can find it on my web site www.holycows.net/datcom. Windows and
Linux executables are available. If you need a model and have some money, I'd
be happy to do it for you.
Bill
billg (at) holycows.net
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